Fluorescent lamps are classified in terms of "T" dimensions with each T unit corresponding to 0.125 inches of diameter. Thus a T-8 lamp has a nominal 1 inch diameter and a T12 lamp a nominal 1.50 inch diameter.
Each type of lamp is designed to operate on a specific type of ballast. That is, while a T8 lamp will operate on a ballast of T8 design, it will operate very inefficiently, if at all, on a ballast designed for T12 lamps, and vice versa. In addition, ballasts are of two types. These are the magnetic type, using the conventional lamination and coil structure, and the electronic type, which uses electronic components to produce a relatively high frequency operating voltage. When using an electronic ballast, the possibility of a lamp of different T value than the ballast design makes proper operation even more difficult.
Accordingly, it would be desirable to produce a fluorescent lamp of one size which can be used with a variety of ballasts, both of the magnetic and electronic type, as well as designed for different size fluorescent lamps.